1. Field of the Invention
The present invention relates generally to a piezoelectric oscillator using an energy-trapped type piezoelectric resonator, and more particularly, to a piezoelectric oscillator in which capacitances are formed.
2. Description of the Prior Art
FIG. 1 is a perspective view showing one example of a conventional piezoelectric oscillator containing load capacitances which is used in a Colpitts oscillation circuit or the like. In a piezoelectric oscillator 1, an energy-trapped type piezoelectric resonator 4 is contained between terminals 2 and 3 having U-shaped cup portions 2a and 3a. The piezoelectric resonator 4 has a structure in which resonance electrodes 5a and 5b are formed on both major surfaces of a piezoelectric plate 4a so as to be opposed to each other in the central region of the piezoelectric plate 4a. The resonance electrodes 5a and 5b are respectively joined to the U-shaped cup portions 2a and 3a of the terminals 2 and 3 by solder joints 6a and 6b. Further, a capacitor 7 is joined to the outer parts of the U-shaped cup portions 2a and 3a.
The capacitor 7 has a structure in which capacitance electrodes are formed on both major surfaces of a dielectric plate 8a. In FIG. 1, only a capacitance electrode 8b on one of the major surfaces is shown. However, a pair of capacitance electrodes are formed and are spaced apart from each other by a predetermined distance on the other major surface. The paired capacitance electrodes are respectively opposed to the capacitance electrode 8b. A terminal 9 is joined to the center of the capacitance electrode 8b.
It has also been known to join a capacitor 7 not to the outer parts of the U-shaped cup portions 2a and 3a but to positions at the height of the central parts of lead-out portions 2b and 3b of the terminals 2 and 3.
In the above described piezoelectric oscillator 1, the terminals 2 and 3 have a complicated shape and the capacitor 7 is joined to the outer parts thereof so as to provide load capacitances. More specifically, in order to provide the capacitances, the additional separately formed capacitor 7 is required, resulting in a relatively large number of components.
Furthermore, the terminals 2 and 3 of complicated shape must be prepared. Moreover, in joining the piezoelectric resonator 4 to the terminals 2 and 3 or joining the capacitor 7 to the outer parts thereof, complicated work is forced to be performed. Consequently, the piezoelectric oscillator 1 becomes substantially higher in cost. It is needed to reduce the cost.